1. Field of the Invention
The present invention relates generally to an optical modulator and, more particularly, to a diffractive waveguide-spatial optical modulator that shifts the phase of incident light by varying the interval between the opposite vertical surfaces of a plurality of reflecting members forming a grating array, thereby forming diffracted light.
2. Description of the Related Art
In the conventional manufacture of optical modulation devices, a device using an acousto-optic effect is referred to as an ultrasonic wave optical modulator. This optical modulator generally uses an ultrasonic wave medium having a uniform optical refractive index, and is operated in such a way as to propagate ultrasonic waves having a uniform period of condensation and rarefaction through the ultrasonic wave medium in a specific direction, introduce laser light into the ultrasonic wave medium at an appropriate incident angle with respect to the direction of propagation of the ultrasonic waves, so that the introduced laser light is reflected by the surface of the ultrasonic waves within the medium and is modulated into diffracted light, and change the output of the ultrasonic waves, so that the state of the condensation and rarefaction of the ultrasonic waves propagating through the medium is changed, thereby changing the intensity of the diffracted light reflected by the surface of the ultrasonic waves and then modulating the laser light.
In the conventional optical modulator, in order to introduce laser light onto the surface of the ultrasonic waves in the medium at the specific incident angle θ, a light source must be installed at a specific inclined angle with respect to the side surface of the ultrasonic wave medium, therefore it is difficult to design and manufacture the system. Furthermore, since a light reflecting surface formed within the ultrasonic wave medium is formed through the aggregation of the ultrasonic waves, the light reflecting surface cannot act as a desirable reflecting surface. In particular, there is a problem in that the output of ultrasonic waves is reduced due to the dispersion of ultrasonic waves that occur within the ultrasonic wave medium. Moreover, there is a disadvantage in that a light absorbing element must be installed outside the ultrasonic wave medium to absorb non-modulated light. Furthermore, when the laser light is incident on the ultrasonic wave medium, the loss of light due to the reflection of light by the surface of the medium cannot be avoided. Moreover, when high-power laser light, such as Ar+laser light or Kr−laser light, is employed, heat generated within the ultrasonic wave medium influences the ultrasonic waves, therefore the modulation of light intensity becomes unstable.
Meanwhile, the conventional optical modulator has problems in that the width of a light beam is restricted in the direction of propagation of the ultrasonic waves and the switching rate is restricted due to time delay at the relatively low propagation speed of the ultrasonic waves.